Phosphopantetheinyl transferases (PPTs) modify their substrate proteins by the addition of a phosphopantetheinyl group derived from coenzyme A. Three PPTs are present in S. cerevisiae: LYS5 (PPTA) is required for the activation of alpha-aminoadipate reductase (an enzyme of the lysine biosynthesis pathway), as well as being important for siderophore and polyketide synthesis; PPT2 (PPTB) pantetheinylates mitochondrial acyl carrier protein (ACP), which is involved in mitochondrial fatty acid biosynthesis; and FAS2 fatty acid synthase alpha subunit, which is a multi-domain protein with a PPT function involved in cytoplasmic fatty acid synthesis. These PPTs are also found in other fungi, such as Aspergillus fumigatus and Candida albicans, and homologues of PPTA and PPTB are found in bacteria, with PPTAs resembling the surfactin synthetase-activating enzyme (sfp) family of bacterial proteins, and PPTBs resembling the bacterial acyl-carrier protein synthases. PPTA, but not PPTB, is found in animals.